Generally in a hydraulic work machine such as a hydraulic excavator, a hydraulic pump is rotationally driven by an engine, and a hydraulic actuator such as a hydraulic cylinder is operated by a hydraulic fluid delivered from the hydraulic pump. Examples of such a hydraulic drive system mounted in a work machine are disclosed in Patent Documents 1 and 2.
In the hydraulic drive system disclosed in Patent Document 1, the hydraulic fluid delivered from one hydraulic pump is divided and supplied to a plurality of actuators, thereby allowing a combined operation.
On the other hand, the hydraulic drive system disclosed in Patent Document 2 is equipped with two engine-driven hydraulic pumps and one electric hydraulic pump, and the actuators are driven by different hydraulic pumps, whereby operational independence in a combined operation is realized.